NO. I GROWTH LAYERS IN TREE BRANCHES CLOCK ET AL. 21 



or macroscopic block was preserved from the immediate vicinity of 

 the a block, it was given the designation A. 



Measurements made on tip growth of branches were taken either 

 weekly or annually. The weekly records were made throughout the 

 entire warm season or else over a calendar year. Annual measure- 

 ments were carried on for a minimum of one year to a maximum of 

 four years. In addition to these more or less periodic measurements, 

 the amount of tip growth was customarily recorded whenever any ex- 

 perimental work was performed. The purpose of the tip-growth meas- 

 urements was not primarily to determine the amount of such growth, 

 but actually to determine the relationship between the number of tip 

 flushes and the number of diameter flushes, and the relative amounts 

 of each. 



As an extension of tip-growth measurements, phenologic observa- 

 tions were carried on, in some cases daily, in others weekly. These 

 were made not only on trees which were later sampled, but also on the 

 general woody vegetation of the area. The phenomena observed in- 

 cluded the start of tip elongation, leafing out, development of cones 

 and flowers, progress of different types of growth, branching, setting 

 of buds, resumption of tip growth, and pest attacks. Also, informa- 

 tion was gathered on late frosts, temperature fluctuations, and rain- 

 fall. 



Branches frozen artificially (Studhalter and Glock, 1942) received 

 an injury which, together with recovery therefrom, later appeared in 

 the xylem and could be used as a reference to relate the injury to the 

 exact time of growth-layer formation. In addition to such "internal 

 tagging," artificial freezing yielded information on the nature of frost 

 injury and the recovery of living tissue from the effects of different 

 intensities of injury. 



When observation and experimentation had been completed on any 

 branches, they were removed from the trees, and blocks were cut 

 from them. The actual time of removal depended upon the purpose 

 the experiments were intended to serve. Many, of course, were taken 

 during the winter which is supposedly the season of least growth. In 

 this way, postseasonal growth could be detected. Those blocks taken 

 at various times during the growing season permitted us to identify 

 multiple diameter flushes. In several instances, a series of similar 

 branches was removed from the tree, one being taken every two weeks. 

 In connection with the freezing experiments, many different branches 

 on a tree were artificially frozen at one time ; they were then removed 

 one at a time at successively longer intervals in order to determine the 



